The present invention relates generally to an auxiliary or primary control structure, and more particularly to a forward pivoted full flying control tail boom hinged with a fuselage/wing of an aircraft.
Lift is a mechanical force generated by interaction and contact between a solid body and a fluid for holding an aircraft in the air. For an aircraft, the lift is typically generated by the deflecting down the air flow, then the air deflects the airfoil up based on the Newton's Third Law of Motion. In another approach, by producing more movement of the air towards the top surface of a wing, a higher velocity of wind on the top side of the wing and a lower velocity of wind on the underside of the wing are resulted. This normally achieved by configuring the wing with a curved shape. According to Bernoulli's Law, the lower velocity on the underside of the wing creates a higher pressure, and the higher velocity creates a lower pressure to pull the wing up.
The amount of lift generated depends on how much the flow is turned; and therefore, the aft portions of wings of most aircrafts are designed with hinged sections to control and maneuver the aircrafts. FIG. 1 shows a typical airplane 10 including a fuselage 12, a pair of wings 14, and a horizontal fixed stabilizer 16 at the tail of the fuselage 12. Hinged at the leading edge of the wings 14 are a pair of slats 18, and hinged at the trailing edge of the wings 14 are a pair of flaps 20 for generating and adjusting the lift of the airplane 10 and a pair of ailerons 24. The areas of the ailerons 24 are relatively small compared to the flaps 20. In addition to the wings 14, the tail 16 may also control the lift by hinging a pair of elevators 22 at the trailing edge of the stabilizer 16. The major part of the lift comes from the wings 14, but the horizontal stabilizer 16 also produces some lift which can be varied to maneuver the aircraft. By deflecting the flaps 20 and the elevators 22 down, more lift is are generated. On the contrary, if either the flaps 20 or the elevators 22 are deflected up, less lift (or negative lift) is generated. Based on stability concern for the aircraft 10 as shown in FIG. 1, the aerodynamic center is typically located aft of the center of gravity (c.g.). Therefore, when the flaps 20 and/or the elevators 22 are deflected down to increase lift, a counterclockwise rotation about the center of gravity of the airplane 10 is generated. On the contrary, when the flaps 20 and/or the elevators 22 are deflected up to decrease lift, a clockwise rotation about the center gravity of the airplane 10 is created. The pitch motion, that is, the rotation about the center of gravity created by the deflection of the aft section of the wings thus results in an opposite inclination of the intended motion of the airplane, which is further described as follows.
In addition to the shape of the aircraft, the lift also depends on how the aircraft moves through the air, that is, the inclination of the aircraft. The inclination is normally expressed by the angle that the airfoil inclined from the flight direction, which is referred as the angle of attack. The larger the angle of attack is, the more amount of lift is generated. However, when the angle of attack reaches a critical point to generate a turbulent flow that lifting off the boundary layer of air from the surface of the airfoil, the lift is lost, and the aircraft is in a stall condition. The relationship between the inclination of the aircraft, that is, angle of attack, and the lift is as shown in FIG. 2.
For the airplane 10 as shown in FIG. 1, the elevators 22 are often used to control the pitch motion. That is, when more lift is generated by the wings 18, instead of being deflected down to generate more lift, the elevators 22 are deflected up to eliminate the pitch motion. Accordingly, the upward deflection of the elevators 22 negates the lift required for the intended motion of the airplane 10. It is very unlikely that such kind of airplane can attain the maximum lift potential and the trimming condition at the same time.
In addition to the pitch motion generated by the deflection of the flaps 20 and the elevators 22 of the wings 14 and the tails 16, roll motion will be caused by the deflection of the pair of the ailerons 24. The ailerons 24 are normally deflected in pair, with individual ailerons deflected in opposite directions. For example, when one of the ailerons 24 is deflected up to cause one of the wing tips moving down, the other of the ailerons 24 is deflected down to cause the other wing tip moving up. The airplane 10 is thus banked, and the flight path of the airplane 10 is curved. The geometry of the ailerons 24 are normally symmetric to generate a pair of substantially identical forces. However, considering the banking motion of the aircraft 10, the forces generated by the ailerons 24 produces a torque to cause the aircraft to spin about the principle axis of the aircraft 10. The spinning motion about the principal axis of the airplane 10 generates roll motion, which is typically controlled by the ailerons 24 operated to negate the banking motion of the aircraft 10.
On some lately developed aircrafts such as the all-wing aircrafts that require high ratio of lift coefficient to drag coefficient (L/D), tails are often eliminated to minimize drag that resists the motion of the aircrafts. The wings are thus the only structure that can deflect the air flow to generate more lift; and at the same time, the only structure to trim the aircrafts. As is well known to those skilled in aerodynamic design, the lift is determined by a product of a lift coefficient, the density of air, square of velocity, and the area of the wings. The lift coefficient incorporates the dependencies of the shape and the inclination of the aircraft. Therefore, to design a high altitude loitering aircraft, a high cruise lift coefficients (CL) is required for efficiency. As mentioned above, in aircrafts with the maximum ratio of lift to drag such as the all-wing aircrafts, tail area is minimized or even eliminated, the lift coefficient thus solely depends on the shape of the wing and the inclination of the aircraft caused by the deflection of the wing. Therefore, the all-wing aircrafts are further limited in their ability to trim to the higher angles of attack required to achieve their maximum lift coefficients. In other words, the all-wing aircrafts may be unable to efficiently counter the pitching moment while attaining the maximum lift potential.